Check your Preferences/Memory settings (Alt/Option + Ctrl/Cmnd + 😉 and make sure that the memory allocated to other apps is a multiple of 4 GB. You want 4, or 8 for other apps. You might get away with 2, of 6, but odd numbers seem to cause problems.
If that does not fix the problem post a screenshot using the icon in the toolbar that looks like a mountain scene with the sun in the sky and give us workflow, system, and AE version details.
Thank you for the response. From what I see from the activity monitor there is 3.22GB for general application memory. This doesnt seem to be something I can change though ?
The forum acts up and won't download attachments. you need to provide the image in a different way from Googtle Drive or whatever. Also provide exact system info and details about the project.